The invention relates to a switching network for selective through-connection of signals of high band width.
In such a broad band switching network, the cross point or coupling point circuits, whose function is to selectively connect input lines to output lines of the switching network can be formed by means of linkage elements realized in ECL technology, in view of the smallest possible switching times or, respectively, of the preferably pulse-modulated signals with signal frequencies, of, for example, up to more 80 MHz to be through-connected (cf. Pfannschmidt: "Arbeitsgeschwindigkeitsgrenzen von Koppelnetzwerken fur Breitband-Digitalsignale", Dissertation, Technical University Braunschweig, 1978; German AS No. 2,828,662).
Given such a broad band switching network, television programs can be switched, for example, to subscribers who wish to receive such programs, as is involved in recent developments of telecommunications which lead to broad band communication networks with subscriber lines formed by means of light waveguides, whereby a star network of light waveguides with one light waveguide per dwelling unit proves favorable at the subscriber level, said light waveguide connecting a broad band switching location (expediently spatially united with the nearest telephone switching location) to the dwelling of the subscriber and via which all telecommunication services for the appertaining dwelling unit are sequenced, whereby offering, for example, at least approximately the following communication possibilities comes into consideration for a dwelling terminal which does justice to future developments:
three video channels for three video receivers with independent access to all television signal sources which can be reached by the switching location or, respectively, television programs which are available in the switching location, PA1 three return channels for program selection and, under certain conditions, for sequencing interactive services, PA1 as well as a greater number of VHF radio channels (stereo) (ntz, 32 (1979) 3, pages 150 through 153).
In such a broad band signal switching center, under certain conditions, a multitude of subscriber terminals must, on the one hand, be able to be connected simultaneously to one and the same broad band signal source, whereas, on the other hand, one must proceed therefrom that the individual broad band signal sources are not to be loaded too low impedance and are not to be loaded with circuit capacitances which are all too great, i.e., are not to be loaded with a randomly great number of directly connected cross point switches or, respectively, subscribers reached via these cross points switches; the invention reveals a way to do justice to this in an expedient manner.